Many aircraft include jet engines, such as turbojet and turbofan jet engines, to provide thrust to move the aircraft, both in flight and on the ground. Generally, when an aircraft is on the ground and not moving, even for relatively short periods, the engines are turned off. However, in some instances, it may be desirable to keep the engines running. For example, in some military contexts, it may be desirable to land an aircraft only long enough to load, or reload, the aircraft with various equipment, supplies, and/or personnel. In such instances, it may be desirable to cool the engine exhaust to a level at or below a particular value, to alleviate discomfort for ground personnel.
The exhaust from turbojet and turbofan engines can be quite hot and noisy. If the jet engine is positioned relative to the airframe such that the hot exhaust impinges on the airframe, the hot exhaust can cause undesirable temperature-induced effects on the material properties of the impinged parts. As a result, the impinged parts may need to be constructed of one or more materials that can withstand high temperatures. This can lead to increased costs. In some cases, even such high-temperature materials may not be sufficient, and thus steps must be taken to prevent impingement or to mitigate the effect of impingement.
A number of different approaches have been used to prevent impingement, or to mitigate, jet engine exhaust gas impingement on airframe surfaces. One attempted solution is to forcibly mix the turbine engine core exhaust with relatively lower-temperature fan bypass air prior to exhausting the mixed exhaust stream out the back end of the engine, so that the resulting exhaust stream has a lower temperature. Another attempted solution is to include a core exhaust thrust reverser that can be selectively deployed and stowed. A core thrust reverser, when deployed, redirects the core exhaust outwardly and forward.
Although each of the above approaches is generally effective, each suffers certain drawbacks. For example, the forcible mixing approach may rely on a long, costly, and heavy bypass duct nacelle configuration to accommodate the mixing structure that joins and mixes the turbine exhaust and bypass air, which can potentially increase costs. Moreover, this approach can cause a reduction in overall engine efficiency. The core thrust reverser may also be a relatively heavy component, and relatively costly to manufacture and install. In addition, because the core thrust reverser includes various moving components, it can exhibit high maintainability, which can further increase overall costs.
Hence, there is a need for a system that provides jet engine exhaust cooling that is relatively lightweight, and/or relatively inexpensive to manufacture and install, and/or includes little if any moving parts, and/or provides increased reliability relative to current systems and components. The present invention addresses one or more of these needs.